1. Field of the Invention
The present invention relates to an image capturing apparatus for guiding light emitted from a light-emitting device to an object, irradiating the object and image capturing the object, and more particularly an image capturing apparatus cutting off the invasion of light to an image capturing unit outside an image capturing range even when disposing the light-emitting device close to the image capturing unit, and obtaining a clear image.
2. Description of the Related Art
An image capturing apparatus for image capturing a predetermined range of an object by irradiating the object with uniform light is widely used. In an image processing system using an image captured by such the image capturing apparatus, a clear image is particularly required.
For example, with the development of biometric technologies in recent years, there have been provided a variety of apparatuses for personal identification, which captures an image of a portion of a human body by which an individual can be distinguished and recognize a characteristic of a living body, for example, fingerprints of limbs, eye retinas, face and blood vessels.
In particular, blood vessels and skin patterns of a palm and a finger are suitable for reliable personal authentication, because a relatively large amount of personal feature data may be obtained therefrom. Further, it is believed that the patterns of blood vessels (veins) do not change from the time of an embryo throughout the lifetime of any person, and that no identical pattern exists among any persons without exception, which are therefore suitable for personal authentication.
For such the biometric authentication or the like, it is necessary to image an object (a portion of a human body in case of the biometric authentication) in a non-contact manner. For this purpose, image capturing apparatus emits light producing uniform light intensity in a certain image capturing range (distance and area), receives the reflected light of the above image capturing range by a sensor, and outputs a captured image signal as an electric signal.
FIGS. 22 and 23 show explanation diagrams of the conventional image capturing apparatus. As shown in FIGS. 22 and 23, image capturing apparatus 100 includes an image capturing (digital camera) unit 120 at the center, and in the periphery thereof, a plurality of light-emitting devices 130-1 to 130-8. The dotted lines shown in FIG. 22 represent the range of the light having uniform intensity emitted from an individual light-emitting device among the plurality of light-emitting devices 130-1 to 130-8.
As such, by disposing a plurality of (here, eight) point light sources in the periphery of image capturing unit 120, the image capturing range of image capturing unit 120 can be irradiated with the light of uniform intensity. Meanwhile, as shown in FIG. 23, the image capturing unit 120 includes a photoelectric conversion unit 122 such as a CMOS sensor, and an optical system 124 such as a lens. Since the photoelectric conversion device 122, which is a plane photodetector device, has a predetermined light receiving area, a predetermined optical distance is required to guide the reflected light of the image capturing range onto the light-receiving plane of the photoelectric conversion device 122. For this purpose, a lens 124 such as a fisheye lens is disposed between the photoelectric conversion unit 122 and the object, so that an image of the predetermined image capturing range is projected onto the light-receiving plane of the photoelectric conversion device 122.
Thus, conventionally, in order to irradiate the object with each point light source element 130-1 to 130-8 by sharing a predetermined image capturing range, the point light source elements 130-1 to 130-8 have been disposed apart from each other, as shown in FIG. 22. Also, in order to supply the light of predetermined uniform intensity to the image capturing range, the point light source elements 130-1 to 130-8 have been disposed closer to the object than the photoelectric conversion device 122, as shown in FIG. 23 (referring to the International Patent Publication No. WO 2004/088588, FIGS. 1 and 6).
In the above conventional image capturing apparatus, as described earlier, the point light source elements 130-1 to 130-8 are disposed apart from each other, and closer to the object than photoelectric conversion device 122, as shown in FIG. 23. Therefore, it is difficult to miniaturize the image capturing apparatus. Also, there is a restriction when incorporating the image capturing apparatus into equipment.
If light-emitting devices which generate high light intensity is used, it becomes possible to dispose the light-emitting device close to the image capturing unit 120. However, the light-emitting device generating high light intensity is expensive and has large power consumption, which is therefore not suitable for a small-sized low-cost image capturing apparatus.